Absolute Dating: a Measure of Time

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Absolute Dating: A Measure of Time Objectives • Describe how radioactive decay occurs. • Explain how radioactive decay relates to radiometric dating. • Identify four types of radiometric dating. • Determine the best type of radiometric dating to use to date an object. I. Radioactive Decay A. What Is Radioactive Decay? Radioactive isotopes tend to break down into stable isotopes of the same or other elements in a process called radioactive decay. B. Dating Rock—How Does It Work? An unstable radioactive isotope is called the parent isotope. The stable isotope produced by the radioactive decay of the parent isotope is called the daughter isotope. To date rock, scientists compare the amount of parent material with the amount of daughter material. The more daughter material there is, the older the rock is. II. Radiometric Dating A. What Is Radiometric Dating? Determining the absolute age of a sample, based on the ratio of parent material to daughter material, is called radiometric dating. B. Rate of Decay If you know the rate of decay for a radioactive element in a rock, you can figure out the absolute age of the rock. A half-life is the time that it takes one-half of a radioactive sample to decay. III. Types of Radiometric Dating A. Potassium-Argon Method This method is used mainly to date rocks older than 100,000 years. B. Uranium-Lead Method Uranium-lead dating can be used for rocks more than 10 million years old. C. Rubidium-Strontium Method This method is also used to date rocks older than 10 million years. D. Carbon-14 Method This dating method is used mainly for dating things that lived within the last 50,000 years. .

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